(Question send by F. Georgina, Fairbanks, Alaska)

Randall R. Wickett, professor of pharmaceutics and cosmetic science at the University of Cincinnati College of Pharmacy, explains.

Although many people still desire a suntan[1], we now understand just how damaging exposure to the sun can be. Repeated sun exposure[2] greatly increases skin wrinkling[3] and may even lead to skin cancers. Adding wrinkles while trying to improve appearance[4] is obviously counterproductive[5] and has led to the popularity of so-called sunless tanning products[6].

The active ingredient in sunless tanners[7] is the compound[8] dihydroxyacetone (DHA)[9]. DHA is approved by the Food and Drug Administration[10] for use in externally applied cosmetics[11] intended to impart color to the skin[12]. A three-carbon sugar[13], DHA reacts with amino groups in the proteins of the top layer of the skin[14], called the stratum corneum[15] (SC). The first step is known as the Maillard reaction, the same process that leads to the caramelization of sugars and the browning of bread[16]. But the complete details of the subsequent[17] reactions are still not fully worked out.

Sunless tans[18] are not exactly the same color as natural tans and do not absorb ultraviolet light in the range that causes sunburn[19]. They therefore do not protect against sunburn. The products of sunless tanning also absorb a little less red light than natural skin pigments do and may lead to orange coloration[20] in some cases. This was particularly true of earlier formulations[21], hence[22] the orange appearance of "quick tans" in the past. Modern products contain lower DHA concentrations[23], leading to a "tan" that is more natural looking, albeit[24] not as dark. Some products also contain the natural sugar erythrulose[25], which adds slightly more red for a more natural color.

Sunless tanners are not without drawbacks[26]. Failure to apply the product evenly can lead to inconsistent color[27]. And some users experience an odor[28] that develops during the tanning process, it is a sign that the product is working. But because the odor actually changes during the development of the tan, it is difficult to mask with fragrances[29].

Sunless tans are not permanent[30] because only the SC is stained[31] and we continually shed this layer of the skin through the process of exfoliation[32]. Typically it takes about three weeks for the SC to "turn over" completely. Use of exfoliating scrubs or exfoliating products such as alpha- or beta-hydroxy acids[33] can speed the exfoliation process and thereby shorten the duration of a sunless tan[34].

Sunless tans provide an alternative to sun exposure and tanning booths[35]. They are likely to increase in popularity as we learn even more about the damaging effects of ultraviolet light on skin.

Opracowanie: Agata Papiorek

Źródło: Scientific American www.sciam.com/askexpert_question.cfm

[1] suntan – słoneczna opalenizna.

[2] repeated sun exposure – powtarzająca się ekspozycja na słońce.

[3] greatly increases skin wrinkling – znacząco wzmaga powstawanie zmarszczek.

[4] while trying to improve appearance – próbując poprawić wygląd.

[5] is obviously counterproductive – przynosi oczywiście efekt odwrotny do zamierzonego.

[6] sunless tanning products – samoopalacze.

[7] the active ingredient in sunless tanners – substancja czynna w samoopalaczach.

[8] compound – związek chemiczny.

[9] dihydroxyacetone (DHA) – dixydroksyaceton.

[10] Food and Drug Administration – amerykańska Agencja ds. Żywności i Leków.

[11] externally applied cosmetics – kosmetyki do użytku zewnętrznego.

[12] intended to impart color to the skin – które mają zabarwić skórę.

[13] a three-carbon sugar – sacharyd zawierający trzy atomy węgla.

[14] amino groups in the proteins of the top layer of the skin – grupy aminowe białek w górnej warstwie skóry.

[15] stratum corneum – warstwa rogowa naskórka.

[16] caramelization of sugars and the browning of bread – karmelizacja cukrów i brązowienie chleba.

[17] subsequent – następny, kolejny.

[18] sunless tans – sztuczna opalenizna.

[19] in the range that causes sunburn – w ilości powodującej oparzenia słoneczne.

[20] may lead to orange coloration orange coloration – mogą powodować pomarańczowe zabarwienie.

[21] this was particularly true of earlier formulations – tak było szczególnie w przypadku kosmetyków starszej generacji.

[22] hence – stąd.

[23] modern products contain lower DHA concentrations – współczesne produkty zawierają mniejsze stężenie DHA.

[24] albeit – aczkolwiek.

[25] erythrulose – erytruloza.

[26] not without drawbacks – nie są pozbawione mankamentów.

[27] failure to apply the product evenly can lead to inconsistent color – nierównomierne nałożenie preparatu powoduje nierówne zabarwienie.

[28] experience an odor – czują zapach.

[29] it is difficult to mask with fragrances – trudno jest zagłuszyć go substancjami zapachowymi.

[30] sunless tans are not permanent – sztuczna opalenizna jest nietrwała.

[31] only the SC is stained – barwiona jest jedynie warstwa rogowa naskórka.

[32] we continually shed this layer of the skin through the process of exfoliation – systematycznie pozbywamy się tej warstwy skóry przez złuszczanie.

[33] alpha- or beta-hydroxy acids –alfa i betahydroksykwasy.

[34] and thereby shorten the duration of a sunless tan – i w ten sposób zmniejszyć trwałość sztucznej opalenizny.

[35] tanning booths – solaria.